Wednesday, January 1, 2014

This is
reference model in this model we can identify architectural perspective for
networks.

This is for how
messages should be transmitted between any two points in a telecommunicationnetwork.
(OSI model makes it easier to learn and understand the concepts involved) In
this model have seven layers. They are,

·Application
Layer – Layer 7

·Presentation Layer – Layer 6 User support layers(5,6,7)

·Session Layer –
Layer 5

·Transport Layer – Layer 4

·Network
Layer – Layer 3

·Data Link Layer – Layer 2 Network support layers(1,2,3)

·Physical Layer – Layer 1

Application
Layer – Layer 7

This layer provides a user interface by interacting
with the running application. E-mail, FTP, web browsers are network applications
that run on this layer. Provide services and protocols to applications.

Presentation
Layer – Layer 6

The data conversion takes place at this layer. The
data that it receives from the application layer is converted into a suitable
format that is recognized by the computer. For example, the conversion of a
file from .wav to .mp3 takes place at this layer. Also concerned with the
syntax and semantics of the information transmitted. And also doingEncapsulation of
data for transmission through the network.

Session
Layer – Layer 5

This layer is responsible to establish and terminate
connections between two communicating machines. This connection is known as a
session, hence the name. It establishes full-duplex, half-duplex and simplex
connection for communication. The sessions are also used to keep a track of the
connections to the web server.Session services include:

·dialog control (who transmits next)

·token management (who is allowed to
attempt a critical action next)

·synchronization (check pointing long
transactions so they can continue after a crash)

Transport Layer – Layer 4

This layer provides end-to-end delivery of data
between two nodes or the transport layer is responsible for the delivery of a
message from one process to another. It divides data into different segments
before transmitting it. On receipt of these segments, the data is reassembled
and forwarded to the next layer. If the data is lost in transmission or has
errors, then this layer recovers the lost data and transmits the same. Or Provides
reliable, transparent transfer of data between end points by

•Service port addressing

•Connection controlling

•Flow controlling

•Error controlling

Network
Layer – Layer 3

The main function of this layer is to translate the
network address into physical MAC address. Or the network layer is
concerned with controlling the operation of the subnet. The data has to be
routed to its intended destination on the network. This layer is also
responsible to determine the efficient route for transmitting the Packets to
its destination / determining how packets are routed from source to destination.
While doing so, it has to manage problems like network congestion, switching
problems, etc. The protocols used here are IP, ICMP, IGMP, IPX, etc.

Data
Link Layer – Layer 2

The data link layer is responsible for moving frames
from one hop (node) to the next. And Provides for reliable transfer of
information across the physical link.The main function of
this layer is to convert the data packets received from the upper layer into
frames, and route the same to the physical layer. Error detection and correction
is done at this layer, thus making it a reliable layer in the model. It
establishes a logical link between the nodes and transmit frames sequentially.

Physical Layer
– Layer 1

Physical layer coordinates the functions required to
transmit a bit stream over a physical medium. It defines a number of network
functions, not just hardware cables and cards.As the name
suggests, this is the layer where the physical connection between two computers
takes place. The data is transmitted via this physical medium to the
destination's physical layer. The popular protocols at this layer are Fast
Ethernet, ATM, RS232, etc.

2.TCP/IP
(Transmission Control Protocol/Internet Protocol)

This is the Implementation of OSI model. TCP/IP is a
set of protocols developed to allow cooperating computers to share resources
across a network.The TCP/IP reference model is the network model used
in the current Internet architecture.in this model main two protocols are
Transmission Control Protocol and Internet Protocol. And so many other
protocols are there. TCP/IP services can be divided into two groups:

•services provided to other protocols - IP,
TCP and UDP

•services provided to end users directly
– HTTP

In this model have four layers.

•Application Layer – Layer 4

•Transport Layer – Layer 3

•Internetwork Layer – Layer 2

•Network Interface Layer – Layer 1

Application
Layer

In TCP/IP model, session or presentation layer are
not present. Application layer is present on the top of the Transport layer. It
includes all the higher-level protocols such as TELNET, FTP, DNS SMTP, SSH…

Transport Layer

This layer is responsible for providing datagram
services to the Application layer. This layer allows the host and the
destination devices to communicate with each other for exchanging messages,
irrespective of the underlying network type. Error control, congestion control,
flow control, etc., are handled by the transport layer. The protocol that this
layer uses is TCP (Transmission Control Protocol) and UDP (User Datagram
Protocol). TCP gives a reliable, end-to-end, connection-oriented data transfer,
while UDP provides unreliable, connectionless data transfer between two
computers.

Internet Layer

This layer is also known as the Network Layer. The
main function of this layer is to route the data to its destination. The data
that is received by the link layer is made into data packets (IP datagrams).
The data packets contain the source and the destination IP address or logical
address. These packets are sent on any network and are delivered independently.
This indicates that the data is not received in the same order as it was sent.
The protocols at this layer are IP (Internet Protocol), ICMP (Internet Control
Message Protocol), etc.

Network Interface Layer

This layer corresponds to the OSI's Physical and
Data Link layers. It explains how the data is transmitted from the host,
through the network. The physical connectors like the coaxial cables, twisted
pair wires, the optical fiber, interface cards, etc., are a part of this layer.
This layer can be used to connect different network types like ATM, Token ring,
Ethernet, LAN, etc.

3.Comparison
Between OSI and TCP/IP Model

3.1Main Similarities between OSI and
TCP/IP Model

•They
share similar architecture

Both of the models share a similar
architecture. This can be illustrated by
the fact that both of them are constructed with layers

•They
share a common application layer

Both of the models share a common "application
layer". However in practice this
layer includes different services depending upon each model

•Both
models have comparable transport and network layers

This can be illustrated by the fact that whatever
functions are performed between the presentation and network layer of the OSI
model similar functions are performed at the Transport layer of the TCP/IP
model

•Knowledge
of both models is required by networking professionals

According to article obtained from the internet
networking professionals "need to know both models"

•Both
models assume that packets are switched

Basically this means that individual packets may
take differing paths in order to reach the same destination